JP4732812B2 - A system and method for magnetizing blocks on a magnet assembly of an MRI apparatus. - Google Patents

Description

  The present invention relates to a system and method for magnetizing blocks on a magnet assembly of an MRI apparatus.

  Magnet assemblies have been used to generate a uniform magnetic field for magnetic resonance imaging (MRI) systems. During manufacture of the magnet assembly, an unmagnetized plate including a plurality of rare earth blocks is disposed on the iron yoke, where the unmagnetized plate refers to a plate that is not substantially magnetized. In order to magnetize a plurality of blocks simultaneously, a relatively large magnetic coil is arranged over the entire non-magnetized block, and a large magnetic field is propagated through the block.

However, the use of relatively large magnetic coils to magnetize unmagnetized blocks has several drawbacks. First, large magnetic coils generate a relatively large amount of heat within the magnet assembly block and within the coil itself, and the block and coil must be cooled to maintain their structural integrity. . In order to cool the block, a relatively expensive additional cooling system must be placed adjacent to the magnetic coil. Secondly, large magnetic coils require a large amount of current to generate a large magnetic field, which requires a relatively expensive current driver. Third, large magnetic coils generate a relatively large electromagnetic force on the block and a relatively large reaction force on the coil during the magnetization process. In order to hold the block and coil in the desired position, a relatively large fixture is fastened to the yoke plate, which is relatively expensive.
US Pat. No. 6,664,878

  Accordingly, there is a need for a method of magnetizing blocks on a magnet assembly for use in an MRI system that overcomes one or more of the above disadvantages.

  In accordance with an exemplary embodiment, a system is provided for magnetizing one of a plurality of substantially unmagnetized blocks disposed on a plate of a magnet assembly for use in an MRI apparatus. The system includes first and second arm portions operably coupled to each other. The system further includes a first electromagnetic coil disposed at a first end of the first arm portion, the first electromagnetic coil being at least one unmagnetized block from the first electromagnetic coil. And a magnetic field that propagates through the plate and further through the first and second arm portions, and is configured to magnetize the block.

  In accordance with another exemplary embodiment, a method is provided for magnetizing at least one of a plurality of substantially unmagnetized blocks disposed on a plate of a magnet assembly for use in an MRI apparatus. The method includes disposing the first and second arm portions in close proximity to the first unmagnetized block and plate, respectively, with the first electromagnetic coil coupled to the first arm. Including. Finally, the present invention excites the first electromagnetic coil to penetrate the first unmagnetized block and plate from the first electromagnetic coil, and further penetrates the first and second arm portions. Generating a first magnetic field that propagates to magnetize the first block.

  With reference to FIGS. 1 and 2, an MRI imaging system 10 for generating a digital image of a human body according to an exemplary embodiment is shown. The MRI imaging system 10 includes a housing 11, a permanent magnet assembly 12, a gradient coil assembly 13, a radio frequency (RF) coil assembly 14, a computer 15, a pulse generator 16, a gradient amplifier 17, and a high frequency. (RF) generator 18, radio frequency (RF) amplifier 19, data collection board 20, and radio frequency (RF) receiver 21.

  The RF generator 18 generates a signal in response to the control signal received from the computer 15, and this signal is amplified by the RF amplifier 19 and transmitted to the RF coil assembly 14. In response, the RF coil assembly 14 generates an RF signal that propagates to the human body in the scanning region and induces nuclei in the patient to emit the RF signal, which RF signal is RF Received by the receiver 21. The received RF signal is digitized in the data collection board 20 and then transmitted to the computer 15.

  The pulse generator 16 generates a gradient signal in response to the control signal received from the computer 15, and this gradient signal is amplified by the gradient amplifier 17 and transmitted to the gradient coil assembly 13. In response, the gradient coil assembly 13 generates a gradient magnetic field in the scanning region that is used to spatially encode the acquired signal.

  A permanent magnet assembly 12 is provided to generate a permanent magnetic field that also propagates through the human body located in the scanning region. The magnet assembly 12 includes yoke plates 30 and 32, columns 34 and 36, a plurality of blocks 38, a plurality of blocks 39, and magnetic pole pieces 42 and 44.

  The yoke plate 30 is provided to hold the plurality of blocks 39 and is made of iron. Similarly, the yoke plate 32 is provided to hold a plurality of blocks 38 facing the block 39, which is also made of iron. Both posts 34, 36 are disposed between the yoke plates 30, 32 and are operably coupled to the yoke plates 30, 32 at both ends of the yoke plates 30, 32, respectively.

  2 and 4, the plurality of blocks 38 are disposed on the yoke plate 32 and are made of a rare earth material such as neodymium / iron / boron (NdFeB). As shown, the blocks 38 are substantially cubic and are arranged in rows on the yoke plate 32 to form a substantially circular outer perimeter. After being placed on the yoke plate 32, the block 38 is bonded to the yoke plate 32. Furthermore, when the block 38 is first placed on the yoke plate 32, the block is not magnetized. The system and method for magnetizing the block 38 will be described below.

  The plurality of blocks 39 are disposed on the yoke plate 30 and are made of a rare earth material such as neodymium / iron / boron (NdFeB). As shown in the figure, the blocks 39 have a substantially cubic shape and are arranged in a row on the yoke plate 30 to form a substantially circular outer peripheral portion. After being placed on the yoke plate 30, the block 39 is bonded to the yoke plate 30. Furthermore, when the block 39 is first placed on the yoke plate 30, the block is not magnetized. The system and method for magnetizing this block is described below.

  Referring to FIGS. 5 and 6, pole pieces 42, 44 are optionally coupled to blocks 38, 39, respectively. The pole piece 42 comprises a generally ring-shaped ferromagnetic material such as iron and is bolted onto the block 38 and the yoke plate 32. Similarly, the pole piece 44 includes a generally ring-shaped ferromagnetic body disposed on the block 39 and the yoke plate 30.

  3 and 7, a magnetizing system 60 for magnetizing the blocks 38 and 39 of the magnet assembly 12 according to an exemplary embodiment will be described. The magnetization system 60 includes arm portions 62 and 64, a bracket 66, a movable link portion 68, an electromagnetic coil 70, a voltage supply source 72, and a switch 74.

  The arm portions 62, 64 are provided to form a generally C-shaped assembly adapted to fit over the yoke plate and a plurality of blocks disposed on the yoke plate for the purpose of magnetizing the block. It is done. Each of the arm portions 62 and 64 is made of a ferromagnetic material such as iron or an iron alloy. Specifically, the arm portions 62 and 64 extend substantially parallel to each other. The arm portion 62 includes arm segments 80, 82, and 84 that are operably coupled to each other using bolts, and the arm segments 80, 82, and 84 form a generally U-shaped structure. Arm segment 80 is coupled to a first end of arm segment 82. Further, the arm segment 84 is coupled to the second end of the arm segment 82. As shown, the electromagnetic coil 70 is coupled to the arm segment 80. Arm portion 64 includes arm segments 86, 88, and 90 that are operably coupled together using bolts to form a generally U-shaped structure. Arm segment 86 is coupled to the first end of arm segment 88. Further, the arm segment 90 is coupled to the second end of the arm segment 88. The electromagnetic coil 70 and the arm segment 86 are arranged at a predetermined distance (D) from each other, and this distance (D) is substantially equal to the thickness of the yoke plate 32 and the block 38. Furthermore, the arm segments 84, 90 extend toward each other and form an air gap 105 therebetween.

  A bracket 66 is provided to operably couple the arm portion 62 to the arm portion 64. The bracket 66 is made of a non-magnetic material and includes bracket portions 100 and 102 that face each other and are substantially parallel to each other. The bracket portions 100, 102 are coupled to each other via a bracket plate 104 disposed at the first end of each of the portions 100, 102. Bracket portions 100 and 102 are further coupled to arm segments 84 and 90, respectively. The bracket 66 further includes a movable member 68 that is movable between the bracket portions 100, 102 using the push rod 106. The movable member 68 is made of iron or an iron alloy. When the movable member 68 is in the first operating position, the member 68 is disposed in the air gap 105 between the arm segments 84, 90 to allow electromagnetic flux to flow between the arm portions 62 and 64. . When the movable member 68 is moved to the second operating position away from the arm segments 84, 90, an air gap 105 is formed to prevent electromagnetic flux from flowing between the arm portions 62 and 64.

  Referring to FIG. 7, a voltage source 72 is provided for exciting the electromagnetic coil 70 through a switch 74. When the switch 74 is in the closed operating position, the electromagnetic coil 70 preferably generates an electromagnetic field of about 1-4 Tesla. Of course, in other embodiments, the electromagnetic field generated by the electromagnetic coil 70 can be greater than 4 Tesla or less than 1 Tesla. Furthermore, when the switch 74 is in the open operating position, the electromagnetic coil 70 no longer generates an electromagnetic field.

  Referring now to FIG. 8, a method for magnetizing blocks in the magnet assembly 12 using the magnetizing system 60 will be described. Specifically, the method will be described with respect to a method of magnetizing two of the plurality of blocks 38. However, it should be noted that all of the plurality of blocks 38 will be magnetized by iteratively repeating the following method. Further, after magnetizing each of the plurality of blocks 38, the method will be repeated iteratively for each of the plurality of blocks 39.

  In step 130, the arm portions 62, 64 are disposed adjacent to the first unmagnetized block 38 and the iron plate 32, respectively, with the electromagnetic coil 70 coupled to the arm portion 62.

  In step 132, the electromagnetic coil 70 is energized to generate a first magnetic field that propagates from the electromagnetic coil 70 through the first unmagnetized block 38 and plate 32 and through the arm portions 62, 64. And magnetize the first block 38.

  In step 134, after the electromagnetic coil 70 is excited for a predetermined time, the coil 70 is demagnetized.

  In step 136, the movable link member 68 is moved away from the area between the arm portions 62, 64 to form an air gap between the arm portions 62, 64.

  In step 138, the arm portions 62, 64 are placed proximate to the second non-magnetized block 38 and the iron plate 32, respectively.

  In step 140, the movable link member 68 is moved into the area between the arm portions 62, 64 to fill the air gap between the arm portions 62, 64 to operably couple the arm portions 62, 64 together.

  In step 142, the electromagnetic coil 70 is energized to generate a second magnetic field that propagates from the electromagnetic coil 70 through the second unmagnetized block 38 and plate 32 and through the arm portions 62,64. Then, the second block 38 is magnetized.

  In step 144, after the electromagnetic coil 70 is excited for a predetermined time, the coil 70 is demagnetized.

  Finally, in step 146, the movable link member 68 is moved away from the area between the arm portions 62, 64 to form an air gap between the arm portions 62, 64.

  9 and 10, a magnetizing system 160 for magnetizing the blocks 38 and 39 of the magnet assembly 12 according to another exemplary embodiment will be described. The magnetization system 160 includes arm portions 62 and 162, a bracket 66, a movable link portion 68, an electromagnetic coil 70, a voltage supply source 72, a switch 74, and an electromagnetic coil 164.

  The main difference between magnet assembly 160 and magnet assembly 12 is that magnet assembly 160 includes a second electromagnetic coil (ie, electromagnetic coil 164). Further, the magnet assembly 160 includes an arm portion 162 instead of the arm portion 64. Arm portion 162 includes arm segments 166, 168 and 170. Arm segment 166 is operably coupled to arm segment 168 at a first end of arm segment 168. Further, arm segment 170 is operatively coupled to the second end of arm segment 168. Segment 170 extends toward arm segment 84 and forms an air gap therebetween. Further, the electromagnetic coil 164 is operably coupled to the arm segment 166. The distance (D 2) between the electromagnetic coil 70 and the electromagnetic coil 164 is substantially equal to the thickness of the yoke plate 32 and the block 38.

  A method for magnetizing blocks in the magnet assembly 12 using the magnetizing system 160 will now be described with reference to FIGS. Specifically, the method will be described with respect to a method of magnetizing two of the plurality of blocks 38. Note, however, that iterating all of the blocks 38 by iteratively repeating the following method. Further, after magnetizing all of the blocks 38, the method will be repeated iteratively for each of the plurality of blocks 39.

  In step 180, the arm portions 62, 162 have the first unmagnetized block 38 and iron plate, respectively, with the electromagnetic coil 70 coupled to the arm portion 62 and the electromagnetic coil 164 coupled to the arm portion 162. 32 is arranged in the vicinity.

  In step 182, the electromagnetic coils 70, 164 are energized to generate a magnetic field that propagates from the coils 70, 164 through the first unmagnetized block 38 and plate 32 and through the arm portions 62, 162. And magnetize the first block 38.

  In step 184, after the electromagnetic coils 70 and 164 are excited for a predetermined time, the coils 70 and 164 are demagnetized.

  In step 186, the movable link member 68 is moved away from the area between the arm portions 62, 162 to form an air gap between the arm portions 62, 162.

  In step 188, the arm portions 62, 162 are placed proximate to the second unmagnetized block 38 and the iron plate 32, respectively.

  In step 190, the movable link member 68 is moved into the area between the arm portions 62, 162 to fill the air gap between the arm portions 62, 162 to operably couple the arm portions 62, 162 to each other.

  In step 192, the electromagnetic coils 70, 164 are energized to generate a magnetic field that propagates from the electromagnetic coils 70, 164 through the second unmagnetized block 38 and plate 32 and through the arm portions 62, 162. And magnetize the second block 38.

  In step 194, after the electromagnetic coils 70 and 164 are excited for a predetermined time, the coils 70 and 164 are demagnetized.

  Finally, in step 196, the movable link member 68 is moved away from the area between the arm portions 62, 162 to form an air gap between the arm portions 62, 162.

  The present system and method for magnetizing a plurality of substantially unmagnetized blocks of a magnet assembly for use with an MRI apparatus provides significant advantages over other systems and methods. Specifically, the present system and method provide the technical effect that it is possible to magnetize individual blocks of a magnet assembly using a relatively simple magnetizer. As a result, large fixtures and current drivers for magnetizing multiple blocks simultaneously are no longer necessary.

  While embodiments of the invention have been described with reference to exemplary embodiments, various modifications can be made to the elements of the invention without departing from the scope of the invention. Those skilled in the art will appreciate that equivalents can be substituted. In addition, many modifications may be made to the teachings of the invention to adapt to a particular situation without departing from the scope of the invention. Therefore, the present invention is not limited to the embodiments disclosed for carrying out the present invention, and the present invention includes all embodiments belonging to the technical scope of the intended claims. Intended. Furthermore, the use of terms such as first, second, etc. does not indicate any order of importance; rather, terms such as first, second, etc. are intended to distinguish one element from another. Used for. In addition, the use of non-numerical terms does not indicate a quantitative limitation, but rather indicates that there is at least one of the items listed. Further, the reference numerals in the claims corresponding to the reference numerals in the drawings are merely used for easier understanding of the present invention, and are not intended to narrow the scope of the present invention. Absent. The matters described in the claims of the present application are incorporated into the specification and become a part of the description items of the specification.

1 is a schematic diagram of an MRI imaging system. FIG. 2 is a schematic view of a permanent magnet assembly used in the MRI imaging system of FIG. 1. 1 is a schematic diagram of a magnetization system according to an exemplary embodiment. FIG. FIG. 3 is a schematic view of a yoke plate and a block used in the permanent magnet assembly of FIG. 2. FIG. 3 is a schematic view of the permanent magnet assembly of FIG. 2 further including a pole piece. FIG. 3 is a schematic view of the permanent magnet assembly of FIG. 2 further including a pole piece. FIG. 4 is a schematic diagram of an electrical circuit for exciting the magnetization system of FIG. 3. 3 is a flowchart of a method for magnetizing an unmagnetized block of the magnet assembly of FIG. 2 according to another exemplary embodiment. FIG. 3 is a schematic diagram of a magnetization system according to another exemplary embodiment. FIG. 10 is a schematic diagram of an electrical circuit for exciting the magnetization system of FIG. 9. 3 is a flowchart of a method for magnetizing an unmagnetized block of the magnet assembly of FIG. 2 according to another exemplary embodiment. 3 is a flowchart of a method for magnetizing an unmagnetized block of the magnet assembly of FIG. 2 according to another exemplary embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 MRI apparatus 12 Magnet assembly 30, 32 York plate 38, 39 Unmagnetized block 42, 44 Magnetic pole piece 60, 160 Magnetization system 62 1st arm part 66 Bracket 68 Movable part 70, 164 Electromagnetic coil 72 Voltage supply source 105 Air gap 162 Second arm portion

Claims (9)

A system for magnetizing one of a plurality of substantially unmagnetized blocks disposed on a plate (32) of a magnet assembly (12) for use in an MRI apparatus,
First and second arm portions (62, 162) operatively coupled to each other;
A first electromagnetic coil (70) disposed on a first end of the first arm portion (62);
A bracket (66) coupled between the first and second arm portions (62, 162);
A movable part (68) operably coupled to the bracket (66) ;
The first electromagnetic coil (70) penetrates at least one unmagnetized block (38) and the plate (32) from the first electromagnetic coil (70), and further the first and second Configured to generate a magnetic field that propagates through the arm portions (62, 162) to magnetize the block (38) ;
An air gap (105) is formed between the first and second arm portions (62, 162);
The movable portion (68) is positioned within the air gap (105) and configured to form a magnetic field path between the first and second arm portions (62, 162);
system. The system of claim 1, wherein the bracket (66) is constructed of a non-magnetic material. The system of claim 1, wherein the movable part (68) comprises iron or an iron-containing alloy. The system of any preceding claim, wherein the first electromagnetic coil (70) generates a magnetic field having a magnitude of 3-4 Tesla. The system of claim 1, wherein the first and second arm portions (62, 162) are constructed of iron or an iron-containing alloy. The first electromagnetic coil (70) has a contact surface area greater than or equal to the contact surface area of the block (38);
The contact surface of the first electromagnetic coil (70) is disposed adjacent to the contact surface of the block during the magnetization of the block (38).
The system of claim 1. A method of magnetizing at least one of a plurality of substantially unmagnetized blocks (38) disposed on a plate (32) of a magnet assembly (12) for use in an MRI apparatus (10) comprising:
The first and second arm portions (62, 162) are coupled to the first arm portion (62) with the first electromagnetic coil (70), respectively, Placing adjacent to the plate (32);
Exciting the first electromagnetic coil (70), penetrating the first unmagnetized block and plate (32) from the first electromagnetic coil (70), and further, the first and second Generating a first magnetic field that propagates through the arm portions (62, 162) to magnetize the first block;
Including methods. The first and second arm portions (62, 162) are connected to the first arm (62) with the first electromagnetic coil (70), and the first electromagnetic coil (70) is Placing adjacent to the second unmagnetized block and plate, respectively, so as to be arranged adjacent to the two unmagnetized blocks;
The first electromagnetic coil (70) is excited to penetrate the second non-magnetized block and plate from the first electromagnetic coil (70), and the first and second arm portions ( 62, 162) generating a second magnetic field that propagates through and magnetizing the second block;
The method of claim 7 , further comprising: The method of claim 7 , wherein the first electromagnetic coil (70) generates the first magnetic field having a magnitude of 3-4 Tesla.

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